creating seperate category styles

Ok, I don’t know if this is a really bad idea or not, or even if it’s possible, but I was wondering if there’s a way to make each category have a different style/design? Theoretically, could I make a “category-3.php” file and have it refer to a new css file that I create for that category?
Surely somebody has thought about this before. Any examples or ideas would be most welcome.
Cheers

Ps. This is not for my personal site; just thinking about possibilities for a new project I’m starting.